1. Field of the Invention
The present invention relates to an epitaxial growth apparatus and an epitaxial growth method and, in particular, to improvement of a support shaft of a susceptor for supporting a semiconductor wafer during growth of an epitaxial film on the semiconductor wafer.
2. Description of the Related Art
In the field of semiconductor electronics in which products are increasingly required to exhibit high performances and high functionality, quality of an epitaxial wafer significantly influences quality of a resulting product device. An epitaxial wafer is a semiconductor wafer having an epitaxial film formed on a surface thereof by vapor phase epitaxy. A high quality epitaxial film having aligned crystal axes is formed on a surface of a semiconductor wafer in accordance with the regular sequence of atoms thereat.
There has conventionally been used in production of an epitaxial wafer a batch-process-type epitaxial growth apparatus capable of effecting epitaxial growth on plural semiconductor wafers simultaneously. However, such a batch-process-type epitaxial growth apparatus as described above cannot easily adapt to production of large-diameter semiconductor wafers. For this reason, in recent years, it is increasingly common to use a single-wafer epitaxial growth apparatus in which epitaxial growth is effected for a single semiconductor wafer individually. Recently, there has been developed a single-wafer epitaxial growth apparatus for a large-diameter semiconductor wafer, capable of handling a semiconductor wafer having a diameter of 450 mm or more.
FIG. 1 is a schematic sectional view of a conventional single-wafer epitaxial growth apparatus 200. This epitaxial growth apparatus 200 includes a chamber 201, a susceptor 202 for supporting a wafer W placed within the chamber 201, and a susceptor support shaft 203 for supporting the susceptor 202. A supply port 204 for a treatment gas is formed at a side portion of the chamber 201, and an exhaust port 205 is formed at a position of the chamber opposite to the supply port 204. Further, plural halogen lamps 206 as heating sources are radially disposed in each of an upper side region and a lower side region of the chamber 201.
FIG. 2 is a schematic exploded perspective view showing details of the susceptor 202 and the susceptor support shaft 203 described above. The susceptor support shaft 203 includes a support column 207 and support arms 208, and a protrusion 209 and a protrusion 210 for supporting the susceptor 202 are provided on the support column 207 and each support arm 208, respectively. Further, there are formed on the rear surface of the susceptor 202 a recessed portion 211 and a recessed portion 212 at positions corresponding to the protrusion 209 and the protrusion 210, respectively. In this structure, the positioning of the susceptor 202 is effected by aligning the recessed portion 211 formed at a center of the susceptor 202 with the protrusion 209 provided at the support column 207. Yet further, the recessed portions 212 are engaged with the corresponding protrusions 210, respectively, thereby preventing the susceptor 202 from making relative movement around the protrusion 209 in the rotational direction.
By using the epitaxial growth apparatus 200, the semiconductor wafer W is placed on the susceptor 202; the halogen lamps 206 are lit to heat the semiconductor wafer W; and a treatment gas including a carrier gas, a growth source gas, a dopant gas and the like are introduced from the supply port 204 while being exhausted from the exhaust port 205 simultaneously, such that the treatment gas flows in a laminar flow state along a surface of the semiconductor wafer W which has been heated to a predetermined temperature. As a result, an epitaxial film can be grown on the semiconductor wafer W.
However, in the case where the aforementioned epitaxial growth apparatus 200 is used, there arises a problem that an epitaxial film having sufficient thickness is not formed at the center portion of the semiconductor wafer W. In general, the thickness of an epitaxial film formed by epitaxial growth is affected by a temperature of the semiconductor wafer W therebelow. As described above, although the semiconductor wafer W is heated by the halogen lamps 206, heat from the halogen lamps 206 located at the lower portion of the chamber 201 cannot be transferred in a satisfactory manner because, as is obvious from FIG. 1, the rear surface of the semiconductor wafer W is heated through the susceptor 202 and there exist the support column 207 of the susceptor support shaft 203 and the protrusion 209 provided at the top end of the support column 207 at the center portion of the susceptor 202 (i.e. the center portion of the semiconductor wafer W).
In view of the facts described above, JP 2000-124141 Laid-Open discloses a technique in which the protrusion 209 is not provided at the top end of the support column 207 and the positioning of the susceptor 202 is effected by alignment of respective three pairs of the protrusions 210 and the recessed portions 212, so that the heat from the halogen lamps 206 located at the lower portion is not blocked and can reach the center portion of the semiconductor wafer W.
The temperature in the chamber 201 of the epitaxial growth apparatus 200 becomes more than 1000° C. during the epitaxial growth process, and the susceptor 202 and the susceptor support shaft 203 are exposed to such a high-temperature environment. JP 2009-135258 Laid-Open discloses a technique in which a reinforcing member (not shown) is provided to each support arm 208 of the susceptor support shaft 203, among the susceptor 202 and the susceptor support shaft 203, in order to prevent the support arm 208 from being deformed and thus supporting the susceptor 202 in a slanted manner.
JP 2000-103696 Laid-Open discloses a technique in which provision of the protrusion 209 at the top end of the support column 207 is omitted as in JP 2000-124141 and further a position at which the support arm 208 is in contact with the rear surface of the susceptor 202 is shifted toward the inner or the outer side in the radial direction than in JP 2000-124141 for the purpose of uniformly heating the susceptor 202 by the halogen lamps 206 located at the lower portion of the chamber 201.
According to the inventions of JP 2000-124141, JP 2009-135258, and JP 2000-103696 described above, the susceptor 202 can be uniformly heated and an effect of making epitaxial film thickness even is achieved to some extent. However, the effect of making epitaxial film thickness even is not yet sufficient and variation in resistivity distribution within an epitaxial film is still quite large.
As a result of a keen study to make thickness and resistivity distribution of an epitaxial film uniform, the present inventors discovered that, even in a case where the susceptor 202 is uniformly heated, the outer peripheral portion of the susceptor 202 is deflected (in the circumferential direction) due to exposure of the susceptor 202 itself to the high-temperature environment and that a magnitude of such deflection of the susceptor 202 as described is especially large at a portion which is not supported by the susceptor support shaft 203.
In a case where the epitaxial growth process is carried out in a state where the susceptor 202 has partially been deflected at the outer peripheral portion thereof, a space is created between the deflected portion of the susceptor 202 and a semiconductor wafer W placed thereon, whereby the semiconductor wafer W is partially cooled by a carrier gas or the like entering into the space and the temperature of the semiconductor wafer W varies in the circumferential direction thereof. When epitaxial growth is performed at such a surface of the semiconductor wafer W where the temperature varies as described above, the thickness of an epitaxial film grown on the wafer surface and the amount of dopant taken into the epitaxial layer also vary within the wafer surface. In short, deflection of a susceptor significantly affects the thickness distribution and the resistivity distribution of a silicon epitaxial film of an epitaxial wafer. This problem of uneven distribution of resistivity cannot be ignored, in particular, in an epitaxial wafer to which the resistivity standards must be strictly applied.